In the field of communications technologies, to reduce construction costs of a communications system, and also increase a communication capacity of a communications system under an architecture of an existing communications system, the prior art provides a solution of deploying an active antenna system (AAS) in a base station system, so as to satisfy requirements of changing coverage of a base station antenna.
The active antenna system refers to an antenna system in which a downtilt angle of a base station antenna can be adjusted freely, to further change a signal radiation angle of the antenna system in a perpendicular direction, so as to change signal coverage of the antenna system. A difference exists between the active antenna system and a conventional base station antenna system, and lies in that: the conventional base station antenna system is provided with a fixed downtilt angle, and once an antenna is completely installed, signal coverage of the antenna system is fixed; while, in the active antenna system, signal coverage of the base station antenna system can be adjusted freely.
Specifically, in the active antenna system, a working principle that a change of a downtilt angle of a base station antenna may cause a change of signal coverage of an antenna is:
performing signal weighting processing on a demodulation reference signal (DMRS) of a base station antenna by using a precoding parameter W, so that signal coverage of the base station antenna is changed.
For example, signal coverage of a conventional base station antenna obtained through calculation by using the following formula is: R0=HXDMRS+N, where H is a channel matrix, XDMRS is a modulation symbol corresponding to a DMRS reference signal sequence, and N is measured noise of a base station antenna and/or measured interference on a base station antenna.
Signal coverage that is obtained through calculation by using the following formula and obtained after adjustment of a base station antenna in an active antenna system is: R1=HWprecodingXDMRS+N, where the matrix Wprecoding is a precoding matrix.
FIG. 1 is a schematic structural diagram showing a change of signal coverage of an antenna caused due to a change of a downtilt angle of the base station antenna in an active antenna system. As can be seen from FIG. 1, a signal coverage area of R1 is greater than a signal coverage area of R0.
However, it is found during research that: in a process in which a base station provided with an active antenna performs weighting processing on a DMRS signal, the following problem exists:
All base stations perform weighting on a DMRS signal, so that when signal coverage of an antenna is changed, a problem of antenna signal overlapping may occur, which not only easily causes system resource wastes, but also causes that interference may occur in an overlapping area of antenna signals, thereby reducing quality of service of a signal of a communications system.
Therefore, a method for self-adaptively adjusting signal coverage of an antenna is urgently needed to resolve problems of system resource wastes and low quality of service of a signal in an active antenna system.